Coal slurry system

Abstract

A slurry of liquified gas such as carbon dioxide and finely pulverized coal particles is provided in a mixing chamber and discharged from the chamber into a pipeline for conveyance to a power plant. During discharge from the mixing chamber pressurized gas at a sufficiently high pressure is injected above the slurry mix to maintain adequate pressure during discharge and prevent cavitation at the inlet port of a pump employed in the pipeline. The slurry is depressurized at the downstream end of the pipeline by movement through a pressure reducer so that it is decompressed non-adiabatically and the coal and gas particles are separated. The gas remains at a low temperature and is passed in heat exchange relationship with cooling water from the power plant cooling tower to lower the temperature of same and consequently increase the efficiency of the power plant. In another embodiment the gas comprises carbon dioxide and a portion of the cool carbon dioxide is discharged directly into the basin of the cooling tower to reduce the water temperature and provide beneficial cooling water chemistry control.

We claim: 
     
       1. A method of providing a liquified gas coal slurry in a pipeline comprising the steps of: (a) providing a predetermined weight of pulverized coal into a chamber closed to a slurry receiving means;   (b) providing liquified gas in the closed chamber so as to substantially fill the closed chamber with slurry at a predetermined pressure and temperature;   (c) placing said chamber in communication with said slurry receiving means; and   (d) discharging slurry from the lower end of said closed chamber into said slurry receiving means that is at a pressure substantially less than said predetermined pressure while simultaneously injecting a pressure maintaining gas at a temperature slightly above said predetermined temperature and at a pressure that is substantially greater than the pressure in said receiving means into the upper extent of said chamber above the slurry so as to maintain said slurry at a sufficiently high pressure as to prevent flashing of the liquid to vapor during the slurry discharge.   
     
     
       2. The method of claim 1 wherein the liquified gas and said pressure maintaining gas are of the same chemical composition. 
     
     
       3. The method of claim 1 wherein said liquified gas is carbon dioxide. 
     
     
       4. The method of claim 3 wherein said pressure maintaining is carbon dioxide. 
     
     
       5. The method of claim 1 wherein said pressure maintaining gas is injected into the upper extent of said closed chamber at a pressure which exceeds the pressure in the receiving means by at least 50 psig. 
     
     
       6. The method of claim 5 wherein the liquified gas and said pressure maintaining gas are of the same chemical composition. 
     
     
       7. The method of claim 6 wherein said liquified gas is carbon dioxide. 
     
     
       8. The method of claim 7 wherein said pressure maintaining gas is carbon dioxide. 
     
     
       9. The method of claim 1 wherein said pressure maintaining gas is provided by passing liquified gas through a heater. 
     
     
       10. The method of claim 9 wherein said pressure maintaining gas is injected into the upper extent of said chamber at a pressure which exceeds the pressure in the receiving means by at least 50 psig. 
     
     
       11. The method of claim 10 wherein the liquified gas and said pressure maintaining gas are of the same chemical composition. 
     
     
       12. The method of claim 11 wherein said liquified gas is carbon dioxide. 
     
     
       13. The method of claim 12 wherein said pressure maintaining gas is carbon dioxide. 
     
     
       14. The method of claim 1 wherein the pressure maintaining gas is injected into said closed chamber after said closed chamber is charged with the liquified gas coal slurry. 
     
     
       15. The method of claim 1 including the additional steps of: (a) terminating the discharging of said slurry from said chamber while there is still a small quantity of slurry in said closed chamber;   (b) again providing a predetermined weight of pulverized coal into said closed chamber;   (c) again providing a liquified gas in the closed chamber so as to substantially fill the closed chamber with a slurry at a predetermined pressure and temperature; and   (d) again discharging slurry from the lower end of said closed chamber while simultaneously injecting a pressure maintaining gas at a pressure and temperature slightly above said predetermined pressure and temperature into the upper extent of said chamber above said slurry so as to maintain said slurry at a sufficiently high pressure as to prevent flashing of the liquid to vapor during the slurry discharge.   
     
     
       16. The method of claim 1 wherein there is substantially no drop in pressure in said slurry upon discharge from said closed chamber.